irange()与range()或xrange()有何不同? [英] How is irange() any different from range() or xrange()?
问题描述
当我遇到 RangeGenerator 页面时,我正在浏览Python生成器Wiki,该页面讨论了irange()
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I was going through Python Generators Wiki when I came across this RangeGenerator page which talks about irange()
-
这将使我们可以迭代大范围的数字而无需 求助于xrange,这是一个懒惰的列表,而不是生成器.
This will let us iterator over large spans of numbers without resorting to xrange, which is a lazy list as opposed to a generator.
我似乎无法理解该页面上描述的测试套件和实现.我知道range()
在内存中创建一个列表(从Python 2.7的角度来看),而xrange()
是一个生成器. irange()
有什么不同?
I can't seem to understand the test suite and the implementation described on that page. I know that range()
creates a list in the memory (from Python 2.7 point of view) and xrange()
is a generator. How is irange()
any different?
推荐答案
irange()
返回生成器类型,该生成器类型只能在上迭代.没有其他的.对其进行迭代后,生成器将耗尽,无法再次迭代.
irange()
returns a generator type, which can only be iterated over. Nothing else. Once you iterated over it, the generator is exhausted and can not be iterated over again.
Python 2 range()
类型是序列类型,它们支持其他序列也支持的各种操作,例如报告其长度,进行遏制测试和索引编制:
The Python 2 xrange()
type and Python 3 range()
type are sequence types, they support various operations that other sequences support as well, such as reporting on their length, test for containment, and indexing:
>>> xr = xrange(10, 20, 3)
>>> len(xr)
4
>>> 10 in xr
True
>>> xr[0]
10
>>> xr[1]
13
您可以多次遍历这些对象:
You can iterate over these objects more than once:
>>> for i in xr:
... print i,
...
10 13 16 19
>>> for i in xr:
... print i,
...
10 13 16 19
您甚至可以使用 reversed()
函数进行迭代可以有效地反向
>>> for i in reversed(xr):
... print i,
...
19 16 13 10
Python 3 range()
类型是xrange()
的改进版本,它支持更多的序列操作,仍然效率更高,并且可以处理超出sys.maxint
的值(在sys.maxint
中为long
整数) Python 2).
The Python 3 range()
type is an improved version of xrange()
, in that it supports more sequence operations, is more efficient still, and can handle values beyond sys.maxint
(what would be a long
integer in Python 2).
例如,它支持切片,这将为切片的值生成一个 new range()
对象:
It supports slicing, for example, which results in a new range()
object for the sliced values:
>>> r = range(10, 20, 3)
>>> r[:2]
range(10, 16, 3)
您可以像使用其他Python序列一样使用负索引来获取从末开始计数的元素:
You can use negative indices just like you can with other Python sequences, to get elements counting from the end:
>>> r[-2]
16
>>> r[-2:]
range(16, 22, 3)
并且该类型支持相等性测试;如果两个range()
实例产生相同的值,则它们是相等的:
and the type supports testing for equality; two range()
instances are equal if they'd yield the same values:
>>> range(10, 20, 3) == range(10, 21, 3)
True
在Python 2中,生成器irange()
可能唯一的优点是它不会受到xrange()
所受的非长整数的限制:
In Python 2, the only advantage the generator irange()
might have is that it doesn't suffer from the limitation to non-long integers that xrange()
is subjected to:
>>> import sys
>>> xrange(sys.maxint)
xrange(9223372036854775807)
>>> xrange(sys.maxint + 1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
OverflowError: Python int too large to convert to C long
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